An Etymological Dictionary of Astronomy and Astrophysics
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Change in frequency of a wave (light, sound) due to the relative motion of source and receiver. Approaching objects have their wavelengths shortened. Receding objects have emitted wavelengths lengthened.

Doppler, after Christian Andreas Doppler (1803-1853), Austrian physicist who first described how the observed frequency of sound and light waves is affected by the relative motion of the source and the detector; → effect.

The Doppler effect when the relative motion of the source and the observer is comparable to the speed of light. In that case the classical Doppler formula should be corrected for effects of the special theory of relativity (Lorentz transformation).

→ relativistic; → Doppler effect.